1. Field of the Invention
The invention relates to a device for fixing a dental prosthesis to a jaw bone.
A device of this type can be used, for example, for fixing a dental prosthesis which consists of a single, artificial tooth usually composed of a plurality of parts. However, it is also possible to insert two or more devices of the stated genera into one and the same jaw bone, which then together hold a dental prosthesis which forms a group of two or more artificial teeth, and namely, for example, a so-called bridge or an entire prosthetic denture.
2. Description of the Prior Art
Devices known under the trade name BONEFIT have two parts which can be detachably connected to one another, namely a base which can be anchored in the jaw bone and is also referred to as the implant or primary part and an abutment which serves for holding the dental prosthesis and is also referred to as the secondary part. The base is elongated and has an axial blind hole which has a mouth at the end face of the base, which face is opposite the dental prosthesis, and has there a mouth enclosed by an annular surface. The blind hole has a section provided with an internal thread and a conical extension extending away therefrom to the end face. The abutment has an inner part with a thread part possessing an external thread, and with a thick part extending conically away from said thread part. Furthermore, the abutment has an outer part adjacent to the thicker end of the thick part. When the device is in the assembled state, the inner part of the abutment is present in the hole of the base, the thread part of the abutment being screwed to the internal thread of the base and the conical thick part of the abutment fitting firmly in the conical extension of the base. The outer part of the abutment is then outside the base and can project into a dental prosthesis and carry this as well as hold it firmly. In the known BONEFIT devices, the abutment section which is located directly above the end face of the base is usually cylindrical or slightly conical and, together with the inclined annular surface present on the end face of the base, forms a shoulder or neck.
The BONEFIT devices have proven very suitable for applications in which the end face of the base is approximately flush with that surface of the gingiva facing away from the jaw bone, or projects slightly out of the gingiva and is in a supragingival position, and in which a dental prosthesis rests on the shoulder or neck. However, if the abutment has, for example, a retentive anchor for clipping on a denture, an intermediate space may be present between said head and the shoulder. The transverse forces exerted on the denture and other forces must then be transmitted to the base or primary part exclusively by the thread part and the conical thick part of the abutment or secondary part, which may cause undesirably large local stresses. In addition, the gingiva may grow over the shoulder or neck so that pockets which are difficult to clean and in which bacteria may develop form under certain circumstances. Furthermore, and in particular, it would be advantageous in various problem cases to cover the base after insertion completely with the gingiva during a certain healing period. In order to permit covering of the base, the latter can of course be inserted into the jaw bone so deeply that its end faces are approximately flush with the ridge of the jaw bone and can then be temporarily closed with a closure screw. If the gingiva is cut open again after the healing period, the closure screw is removed and the abutment is screwed into the base, the stated shoulder or neck is present below the gingiva after the latter has healed. If the dental prosthesis usually produced by a dental technician thereafter does not fit very exactly and without gaps on the shoulder or neck, there is a considerable danger that free cavities will remain in the shoulder or neck under the gingiva and bacteria will develop in the said cavities. These may interfere with the healing process and cause infections.
In the "Journal of Oral Implantology", Volume XVI, 1990, No. 4, pages 297-301, a device having a base or implant, a connecting element, a spacing shell and an abutment is disclosed. The base is identical or similar to that in the BONEFIT devices. The connecting element has a thinner and a thicker thread part, each having an external thread, a cone present between the two thread parts and an axial threaded hole. The spacing shell has an axial through-hole with an internal thread. The abutment has a thread part with an external thread.
When this device is used, the base can be inserted into a hole in the jaw bone in such a way that the end face of the base is approximately flush with the surface of the jaw bone. After healing of the bone, the thinner thread part of the connecting element can be screwed into the base until the cone of the connecting element fits firmly in the conical extension of the hole of the base. Thereafter, the spacing shell can be screwed onto the thicker thread part of the connecting element, which thread part projects from the base, and the thread part of the abutment can be screwed into the threaded hole of the connecting element. The spacing shell then rests firmly against the end face of the base.
This device disclosed in the "Journal of Oral Implantology" has already proven its worth but has the disadvantage that it has four separate parts, some of which have relatively complicated shapes and in particular possess many threads. The production and assembly of this device are therefore relatively expensive and complicated.